Heidelberg 1999 – scientific programme

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T: Teilchenphysik

T 403: Diffraktion 2

T 403.7: Talk

Tuesday, March 16, 1999, 18:00–18:15, TE10

Small-x Structure Functions in the Eikonal Model — •Arthur Hebecker¹, Wilfried Buchmüller², and Thomas Gehrmann³ — ¹Universität Heidelberg, Institut für Theoretische Physik, Philosophenweg 16, 69120 Heidelberg — ²Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg — ³Universität Karlsruhe, Institut für Theoretische Teilchenphysik, Engesser Str. 7, 76128 Karlsruhe

Small-x deep inelastic scattering is discussed in the framework of the semiclassical or eikonal approach. Both diffractive and inclusive parton distributions are expressed in terms of non-Abelian eikonal factors, which characterize the colour rotation of fast partons penetrating the proton colour field. A simple model for averaging over the relevant field configurations is introduced. Within this model, all parton distributions at some low scale Q₀² are given in terms of three parameters. Inclusive and diffractive structure functions at higher values of Q² are determined in a leading-order QCD analysis. In both cases, the evolution is driven by a large gluon distribution. A satisfactory description of the structure functions F₂(x,Q²) and F₂^D(3)(ξ,β,Q²) is obtained. The observed rise of F₂^D(3) with ξ is parametrized by a non-perturbative logarithmic energy dependence, compatible with unitarity. In our analysis, the observed rise of F₂ at small x is largely due to the same effect.